1. Field of the Invention
The present invention generally relates to an electrical connector, and in particular to a ZIF (zero insertion force) socket connector having a force-balanced structure for eliminating a transverse engaging force acting upon a chip mounted on the socket connector.
2. The Prior Art
Socket connectors for mounting electronic chips to a circuit board are well-known in the electronics field. The socket connector defines a plurality of holes for fixedly receiving conductive terminals therein. The chip has a plurality of conductive pins extending into the holes and electrically engaging with the terminals. Mechanical engagement is formed between the pins of the chip and the terminals of the socket to secure the chip to the socket. The mechanical engagement, however, inflicts damage on the pins and the terminals caused by abrasion therebetween when inserting the pins into the holes.
A zero insertion force (ZIF) socket connector overcomes the abrasion problem by inserting the pins into the holes of the socket connector such that the pins do not initially engage the terminals whereby abrasion during insertion is prevented. The chip is then moved transversely to bring the pins into engagement with the terminals. Examples of ZIF socket connectors are disclosed in Taiwan Patent Publication Nos. 85218817 and 83208396 and U.S. Pat. Nos. 5,492,488 and 5,562,474.
The transverse movement of the chip, however, imparts a transverse engaging force on the pins during engagement with inclined resilient arms of the terminals leading to an unbalanced force and resulting in mechanical and electrical instability between the chip and the connector.
FIG. 1 shows a conventional ZIF socket connector comprising a socket base 62 defining holes 621 therein for accommodating conductive terminals 63. A cover 61 is slidably positioned on the base 62. The cover 61 also defines holes 611 therein corresponding to the holes 621 of the base 62. A lever 64 is rotatably mounted to the base 62 and engages with the cover 61 to shift the cover 61 with respect to the base 62.
Each hole 621 of the base 62 has an expanded opening as shown in FIG. 2. The expanded opening allows a corresponding pin 7 of a chip to be inserted therein with substantially zero insertion force (FIGS. 3A and 3B). By actuating the lever 64, the cover 61 is moved relative to the base 62 thereby driving the pins 7 to move toward and engage with inclined resilient arms 631 of the corresponding terminals 63 (FIGS. 3C and 3D). During this process, the arm 631 is deformed and imparts a transverse engaging force on the pin 7.
Conventionally, the engaging forces of all the pins 7 of the chip are in the same direction which causes a transverse offset of the chip with respect to the socket 62 leading to undesired frictional engagement between the pins 7 and inner walls 6211 of the holes 621 of the socket 62. An additional resistance to the movement of the cover 61 is formed and an excessive force is required to achieve the desired engagement between the pins 7 and the terminals 63. Such an excessive force may damage the socket 62 and the pins 7. As a consequence, unstable mechanical and electrical engagement may result.